1. Technical Field
The invention relates to a procatalyst of a catalyst system intended for the polymerization of olefins comprising a magnesiumhalide-containing carrier, a titanium compound and a dialkylester of phthalic acid. The invention also relates to a method for the preparation of a procatalyst of a catalyst system intended for polymerization of olefins, in which a magnesiumhalide-containing carrier is brought into contact with a titanium compound and a dialkylester of phthalic acid. The invention also relates to the use of a procatalyst of the above-mentioned type together with an organometallic cocatalyst for the preparation of polypropylene.
2. Description of the Related Art
In general a Ziegler-Natta catalyst system is used for the polymerization of olefins, which system consists of a so-called procatalyst and a cocatalyst. The procatalyst is based on a compound of a transition metal belonging to any of the groups IVA to VIII of the periodic table and the cocatalyst is based on an organometallic compound of a metal belonging to any of the groups IA to III(B) of the periodic table (the groups are marked according to Hubbard, see e.g. L. Rompp, 8th Edition, p. 3051).
Generally, to a catalyst system also belongs electron donor compounds improving and modifying the catalytic properties. When stereoselective, high-yield Ziegler-Natta catalysts on solid magnesium compound carrier are prepared organic mono-and diesters are widely used to improve the stereoselectivity of the catalyst. In co-ordination polymerization chemistry these esters are often characterized as internal electron donors.
Of organic diesters the best known in the field are the diesters of phthalic acid. Such alkylphthalates have been presented e.g. in the following publications: EP-268,685 A1, EP-250,244 A2, EP-45,975 A2, EP-86,643 A2, EP-16,141 A1, EP45,977 B1, EP-267,576 A2, EP-206,172 A1, EP-256,865 A1, and EP-261,961 A2. In previous patents the most useful electron donors have been the n-butyl or di-isobutylesteracid of 1,2-benzenecarboxylic acid.
By using alkyl esters of phthalic acid as the electron donor component of the procatalyst of a catalyst system intended for the polymerization of olefins the aim has been to achieve an as stereoselective and high yield catalyst as possible. The improvement of this property is the goal also in the present invention.